| In the fault case of main generator and auxiliary power unit generator,ram air turbine system obtains airflow kinetic energy during aircraft gliding,and provides emergency hydraulic or emergency power for the equipments of aircraft so as to maintain the maneuverability of aircraft.The power quality of ram air turbine AC power generation system directly affects the power supply for key equipments in aircraft.The three-stage variable frequency synchronous generator and generator control unit are the important electrical components of emergency power generation system.This dissertation will take the three-stage variable frequency generator with rated frequencies from 453 Hz to 641 Hz and rated power of 10 kVA as the research object.According to the demand for voltage regulation and system control of AC power generation system,based on the current digital voltage regulation technology and digital sampling technology,this dissertation mainly focuses on the design of generator control unit,digital voltage regulation strategy,sampling of variable frequency AC signal and so on.Firstly,based on the current Simulink model,the mathematical models in d-q axis coordinate system of electrically excited synchronous generator and permanent magnet synchronous motor are established.According to the method of digital sampling and calculation method for root mean square(RMS)value of variable frequency AC signal,the control model of variable sampling period and variable control period is built up,which makes the simulation step of control loop consistent with the actual control cycle,while the simulation step of generator is far shorter than the simulation step of control loop.Aiming at the problem of differential voltage regulation performance of the same PI parameter under different speed and load conditions,a voltage regulation strategy based on fuzzy PI controller is proposed.This strategy sets different PI parameters according to speed and load conditions,and the AC power generation system can obtain better voltage regulation performance in full speed range and load conditions.Secondly,the real-time sampling system of wide variable frequency AC signal and the digital sampling method of AC signal are introduced.For software synchronous sampling method,the theoretical errors under ideal zero synchronization error,synchronization error caused by frequency detection error or change of signal frequency are discussed respectively.At the same time,the theoretical error of asynchronous sampling method is analyzed theoretically,and an asynchronous sampling method based on error correction is proposed.Then the influence of correction method on harmonic RMS is analyzed,and the error caused by asynchronous sampling calculation method is basically eliminated.Experiments on the generator control uint hardware platform verify the correctness of analysis about the two sampling methods.Then,the hardware circuit of the generator control uint is designed,including the main control circuit,auxiliary power supply circuit,signal sampling circuit,excitation main power circuit,dual redundancy CAN communication circuit,28V/open output drive circuit,ground/open output circuit and ground/open detection circuit.Based on the hardware platform,the main program,sampling and voltage regulation program,communication program,protection and self-test program are designed.Finally,a generator control uint applied to RAT power generation system is made,and the self-check,control and protection information of DSP is sent to the upper computer system through dual redundancy CAN communication,which verifies the correctness of the system function.Compared with the conventional PI voltage regulator,the experimental results of the voltage regulation control strategy based on the fuzzy PI regulator are in agreement with the simulation results.It is convenient for parameter debugging under various load changing conditions and can optimize the dynamic response performance of the AC power generation system. |
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